I need to design a simple thrust bearing to support a vertical load. I want to keep the diameter as small as practical, ideally about 3/8 inch or less. The static load will be up to 500 pounds, and the speed of rotation will be around 4 RPM, but the shaft will only rotate 180 degrees and stop for a while, then rotate back 180 degrees. The number of rotations per day will likely be around 10, so 40,000 cycles would probably last 10 years. Initial lubrication can be performed (high pressure grease?), but periodic lubrication is not feasible. The working environment should be reasonably clean, but it may collect some dust over time as it will not be fully sealed unless required.
I am considering a single hardened bearing ball in a Delrin spherical socket. If my calculations are correct, a ball of diameter 1/4 inch with a contact area of about 50% of the sphere would have a surface area of about 0.2 in^2. Delrin has a Young's modulus of 450,000 PSI. Based on these criteria the force of 500 pounds on the ball should produce a pressure of about 2546 PSI. This is far under the yield strength of Delrin. Am I missing something here? I have not been able to find anything on designing such a simple thrust bearing. Attached is a CAD model showing the concept.
Whilst your idea is simple the use of a sphere is of no great benefit unless the load from above was arcing as well as rotating? + you can't use the whole hemisphere for loadbearing as that nearest the load would show less force on the cup as opposed to the point furthest from the load which would show the most! What is wrong with a simple needle roller bearing set up - lube for life with 3 in 1 and simple shield seal - job done?
I would agree with kawazuki. The surface area bearing the load is going to be much less than the surface area of a hemisphere. The majority of the load will be carried near the bottom of the sphere. My first thoughts were to use a needle roller bearing as well.
I wanted to add to my comment above to better support what I was saying. The only time you could consider using the full surface area of the hemisphere is if both bodies can be considered ridged and there is no clearance between the two bodies. I went online and did a little research to see if I could come up with a more accurate calculation to use in this case. If you multiply your initial pressure calculation by 3/2 you will have a more accurate result. It should be in the neighborhood of 3820 psi. https://en.wikipedia.org/wiki/Bearing_pressure You should still be fine with Delrin but it doesn't leave much of a safety factor.
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Need help with thrust bearing design
